The spine is a flexible column formed of a plurality of bones called vertebrae. The vertebrae are hollow and piled one upon the other, forming a strong hollow column for support of the cranium and trunk. The hollow core of the spine houses and protects the nerves of the spinal cord. The different vertebrae are connected to one another by means of articular processes and intervertebral, fibrocartilaginous bodies. Various spinal disorders may cause the spine to become misaligned, curved, and/or twisted or result in fractured and/or compressed vertebrae. It is often necessary to surgically correct these spinal disorders.
The spine includes seven cervical (neck) vertebrae, twelve thoracic (chest) vertebrae, five lumbar (lower back) vertebrae, and the fused vertebrae in the sacrum and coccyx that help to form the hip region. While the shapes of individual vertebrae differ among these regions, each is essentially a short hollow shaft containing the bundle of nerves known as the spinal cord. Individual nerves, such as those carrying messages to the arms or legs, enter and exit the spinal cord through gaps between vertebrae.
The spinal disks act as shock absorbers, cushioning the spine, and preventing individual bones from contacting each other. Disks also help to hold the vertebrae together. The weight of the upper body is transferred through the spine to the hips and the legs. The spine is held upright through the work of the back muscles, which are attached to the vertebrae. While the normal spine has no side-to-side curve, it does have a series of front-to-back curves, giving it a gentle “S” shape. If the proper shaping and/or curvature are not present due to scoliosis, neuromuscular disease, cerebral palsy, or other disorder, it may be necessary to straighten or adjust the spine into a proper curvature.
Generally the correct curvature is obtained by manipulating the vertebrae into their proper position and securing that position with a rigid system of screws, rods, intervertebral spaces, and/or plates. The various components of the system may be surgically inserted through open or minimally invasive surgeries. The components may also be inserted through various surgical approaches to the spine including anterior, lateral, and posterior approaches.
In some circumstances, a tissue retractor may be inserted into a surgical incision to pull tissue away from the surgical site and enlarge the viewing area for the surgeon. Tissue retractors form a surgical corridor including a proximal opening at the incision and a distal opening near the surgical site. Various instruments and implants may be inserted through the corridor. Exemplary tissue retractors may be found in U.S. Pat. No. 7,780,594 entitled “Retractor and Methods of Use” filed Oct. 6, 2006 and U.S. App. Pub. No. 2008/0114208 entitled “Retractor” filed Sep. 24, 2007. The amount of tissue to be retracted depends upon the chosen approach as well as various patient characteristics. For example, in a lateral approach, more soft tissue may be present between the surgical incision and the surgical site near the vertebrae than in a posterior approach. Patient anatomical differences may also require various length retractors. The size, shape, and configuration of the retractor may be chosen based on these as well as other factors.
Tissue retractors typically include two or more elongated blade assemblies with proximal ends attached to a housing that is in turn attached to a surgical table for support. Each blade assembly may be attached to a separate portion of the housing and include various adjustment features for manipulating the blades to adjust and enlarge the viewing area. Often, the tissue retractor may hold the blades close together in a tubular configuration for concentric insertion over dilation tubes along a common longitudinal axis. The portions of the housing may translate or rotate relative to one another to gradually pull the blades apart from one another to expand the surgical opening. In addition, the distal ends of the retractor blades may be angled away from (toe-out) or towards (toe-in) the longitudinal axis to adjust the viewing area at the surgical site.
In order to perform a lateral surgical procedure to implant an interbody spacer, a soft tissue retractor similar to retractor 100 or 100′ may be necessary in order to gain exposure through the psoas muscle. Often, a plurality of dilators is inserted into the patient to begin to open the surgical site. Typically, a 2-, 3-, or a 4-blade retractor system is slid over the dilators and used to expand the soft tissue to expose the surgical site allowing direct visualization for the implant procedure. Due to variances in human anatomy, the retractor must accommodate a range of interchangeable blades of different lengths. In addition, the retractor system should provide the ability to tilt the distal ends of the blades radially outward to create a toe-out condition that provides greater exposure of the surgical site near the spine.
Most systems require retractor removal to change the blades. Therefore, when it is discovered that a different blade length is necessary after insertion, changing the blades may be cumbersome and risk tissue encroachment. Further, most systems employ separate mechanisms for blade attachment and toe out which complicates installation and manipulation of the blades by the user. Further, existing toe-out mechanisms allow blade tilting in only discreet steps, typically of 5, 10, and 15 degrees. Since the blade lengths can be as long as 160 mm, these increments cause large displacement at the distal end of the blade which leads to over distraction of muscle tissue. Last, many blade coupling mechanisms are insufficiently strong and secure to resist the high bending loads generated as the blades are expanded or under toe-out conditions and the tissue resists the expansion.